P-value distribution/volcano plot of line and size effect. Scatter plot with mean expression level (log 10) on the x-axis and – p-value (log 10) on y-axis. Each gene is plotted twice, once for the p-value resulting from the tumor-line effect ANOVA (black) and once for the p-value resulting from the tumor-size effect ANOVA (red). The blue line represents a p-value of 0.01. Genes with a lower p-value (more significant) have a higher – p-value log10. There are far more genes with significant p-values due to differences in the tumor lines than due to changes in tumor size.